390 Fe main side seal questions

1oldtimer

1oldtimer

Well-known member
Fresh rebuild and I haven't started it yet. What's the trick to getting these to seal, so far 2 sets have leaked just by tilting the motor back with oil in the pan. I've looked through google and some said fill with rtv, some said install according to directions and then I also found this:
"Ditch the gasket/rubber seal. I had the same problem getting the rear main to seal. Called Felpro years ago and asked them what gives. They, being Felpro, said to get a cotton mop head that has not been used. Cut a piece off it, more than 12" long. Get some red RTV silicone gasket maker. Smear gobs of the RTV on the mop head thread. Use an old phillips head screw driver and shove the thread down the sides of the rear main. I just rebuilt another 390 this past week. Took about 16" on each side to completely stuff the rear main full.

Its a messy solution, but the first one I did was 15 years ago and is still holding. "


HELP........this thing sucks.
 
I haven't tried anything other then the rubber and nails that the kit comes with twice. The others are from the internet and I'm trying to see if there is another way that's been successful since this is the FE weak spot for oil leaks.
 
Three things you need to know to make the rubber with nails kit work. Clean, clean, clean. Wipe out the block with acetone or laquer thinner. Maybe even sand paper. Whatever it takes to get back to clean metal. The same with the aluminum seal holder. I have had better luck with the cheapy rope seals. My latest 312 has the 45 dollar rubber seal, it seeps worse than the one with the rope seal. I soak the rope for a week, then hammer it in the holder with a 1 1/2 inch socket. Trim the ends. Put one small dab of silicone seal on the bottom of the seal holder, and a dab on the threads of the bolts, and gently torque the bolts to about 30 Ft. lbs. Then lightly oil the rubber side parts, and with a small dab of silicone on the end, tap them in. A gentle smear of sylicone over the whole thing should make it oil tight.
 
so far I've had 3 people tell me that the old rope style seal works better. The one posted above, someone at work used a mop strand with weather stripping adhesive and packed it full. I'm going to try it from the underside as the motor is in the truck now.
 
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